There are several things you can do about the cramps. Initially, follow the excellent stretches mentioned earlier in the thread. A hot bath with Epsom Salts will do wonders, especially if you scent the water with an essential oil or two. You should limit yourself to 15 - 20 minutes for the soak. Consult your doctor if you are sensitive to salts. You'll be soaking in magnesium heptasulfate.
Staying hydrated is also a major player in not having cramps, as is remaining flexible.
One way you can massage your back, actually two ways, is with tennis balls. Begin by taking two tennis balls and shoving them into an old, clean sock. Wrap the rest of the sock in an overhand knot and snug it up against the tennis balls as tightly as you can.
You now have a device that will work on your neck, erectors and lower back. Place the sock on a hard floor and lean back on it from a sitting position before it. The cleft between the tennis balls will allow your spine to travel unencumbered as the sock rolls up and down your back.
Place your feet on the floor, lift your hips, and using your legs - try not to use your arms for balance or assistance as that tends to bring the shoulders forward - move your body so that the balls roll up or down the spine as you wish. This process will occasionally align a subluxation after the muscle has released.
For direct access to the traps, use the third tennis ball from the can. Place your feet about one foot out from a wall with your back toward the wall. Holding the tennis ball in one hand, lean back until your hips are touching the wall and you can place your back against it.
Place the tennis ball above the area that has the strongest desire for release and, leaning forward slowly, allow the tennis ball to find that spot. Then lean back into the tennis ball and take a deep breath, bringing it to that muscle point.. . .hold for eight seconds . . .and exhale fully.
You can then lean forward again and direct the ball further down. When you are done, or wish to target a different area, simply cup your hand and move it to the wall under your hips. Balance the weight on your shoulder and move your hips forward. The ball will fall into your hand, allowing you to repeat the process.
Word of warning about rolling around on the tennis balls -- if you have a dog. Not only will they think it a toy if you leave it about; when you are on the floor supine and your face is at about the same elevation as the water bowl. . . be prepared for a tongue bath!